Remove the update_object() in object_client

The method is not used in long-term, and it is the same as
create_object(). Remove it.
Change-Id: I94a729464ba5e366374e5bee3ada14c223d2f9ac
diff --git a/tempest/services/object_storage/object_client.py b/tempest/services/object_storage/object_client.py
index 33dba6e..5ddfa71 100644
--- a/tempest/services/object_storage/object_client.py
+++ b/tempest/services/object_storage/object_client.py
@@ -42,12 +42,6 @@
         self.expected_success(201, resp.status)
         return resp, body
 
-    def update_object(self, container, object_name, data):
-        """Upload data to replace current storage object."""
-        resp, body = self.create_object(container, object_name, data)
-        self.expected_success(201, resp.status)
-        return resp, body
-
     def delete_object(self, container, object_name, params=None):
         """Delete storage object."""
         url = "%s/%s" % (str(container), str(object_name))